This invention is directed broadly to mercury vapor arc discharge lamps and more particularly to methods for avoidance of soluble mercury pollution of landfills and groundwater upon disposal of such lamps and during TCLP testing for leaching of soluble mercury materials from such lamps. Compositions of matter useful in preventing the formation of leachable mercury in disposal and testing procedures form a part of the invention.
Mercury arc vapor discharge lamps, otherwise commonly known as fluorescent lamps, are standard lighting means. The mercury arc vapor discharge lamp consists of metallic components such as lead wires, connector pins and end caps. The lead wires and portions of the end cap and connector pins are surrounded by a glass enclosure. The interior of the glass enclosure is typically coated with phosphor. Elemental mercury is added to the mercury arc vapor discharge lamp and typically, the elemental mercury adheres to the phosphor. In certain conditions, it has been found that when elemental mercury comes in contact with the metal components in a lamp such as copper and iron containing lead wires, brass pins, or other associated metallic mount components, the elemental mercury is transformed into a leachable form.
In order to address the growing concern that mercury from disposal of fluorescent lamps might leach into surface and subsurface water, the Environmental Protection Agency has established a maximum concentration level for mercury at 0.2 milligrams of leachable mercury per liter of extract fluid. The concentration level for mercury is generally determined by a standard analysis known as the Toxicity Characteristic Leaching Procedure (TCLP), a well known test procedure.
When carrying out the TCLP test, test lamps are pulverized to form lamp waste material similar to that which would result from lamp disposal in land fills or other disposal locations. The ambient conditions in disposal locations may be such as to promote formation of leachable mercury. The TCLP test conditions themselves tend to allow for formation of leachable mercury in amounts greater than the established limit of 0.2 milligrams per liter.
During the disposal of the lamp, and in the TCLP test, the glass enclosure of the lamp is broken. Elemental mercury that is contained in the lamp is then exposed to the metal components in an aqueous environment. Elemental mercury, when exposed to both the metal components and the aqueous environment, is oxidized to leachable mercury. The metal components in the lamp provide the source of oxidizable iron and oxidizable copper that promotes the formation of leachable mercury.
There is concern about the environmental impact of soluble mercury compounds which can leach into ground water sources, rivers, streams, and the like. In the prior art, certain oxidants and reductants are placed in a lamp to alter the form of mercury during the course of the TCLP test. These agents function to remove leachable mercury from the TCLP solution.
Generally, any modification of the lamp components is driven by the need to decrease the amount of leachable mercury. Methods and materials are constantly being sought which decrease the leachable mercury values upon performance of the TCLP extraction test.
The present invention provides a method for preventing formation of leachable mercury compounds during TCLP testing of mercury vapor discharge lamps having an envelope of light transmitting glass and an amount of elemental mercury which comprises incorporating into the lamp structure an amount of pure gelatin or a degradation product of pure gelatin in the form of a discrete button which is effective to substantially prevent formation of ferric and cuprous compounds when iron and copper components of the lamp are exposed to moisture and acidic conditions.
The present invention further provides a mercury vapor arc discharge lamp comprising pure gelatin or degradation product of pure gelatin incorporated in the lamp structure in the form of a discrete button wherein the gelatin is present in a range between about 0.02 grams and about 3 grams per lamp.